As is known, LED sources are increasingly widespread since they are characterized, among other things, by a high energy efficiency and a low power consumption given the same light yield.
LED sources require driving circuits capable of supplying low-voltage d.c. currents. For this reason, in the case where it is desired to supply an LED source through the electrical mains supply, it is necessary to use, within the driving circuit, a switching converter, such as for example a converter of a buck, boost, or flyback type.
The use of switching converters is particularly indicated in the case of professional applications, i.e., in the case of applications where the level of power required is relatively high (for example, higher than 50 W), and where the constraints regarding the package and installation are not stringent. Instead, in the case of applications, for example, in a domestic setting, the power required is low, and integration of switching converters in the driving circuits is problematic since the constructional constraints regarding the LED sources, for example as regards the corresponding plugs, are stringent.
As an alternative to the use of switching converters, less complex solutions have been proposed, also known as AC-LEDs. These solutions have some aspects in common, such as for example: the presence of a rectifier circuit; the presence of a plurality of LED strings, each string being formed by a corresponding number of LEDs connected in series; and the presence of one or more modules, which regulate the current that flows in the strings as a function of the value of the sinusoidal mains voltage. An example of driving circuit of an AC-LED type is described in United States Patent Application Publication No. 2013/0257282 (EP 2645816) (incorporated by reference).
In greater detail, typically a driving circuit of an AC-LED type is configured so that, as the sinusoidal mains voltage increases, the number of LED strings connected in series increases, and consequently also the number of LEDs turned on. Furthermore, as the number of LEDs turned on grows, the driving circuit increases the regulated current. More in particular, the increases in current occur according to discrete levels; the current thus remains constant for a certain time interval, before increasing to the next level. The number of current levels is equal to the number of LED strings.
This having been said, driving circuits of the so-called AC-LED type are effectively characterized by a high constructional simplicity; however, they provide only a fairly good performance in terms of power factor and harmonic distortion, on account of the stepwise currents generated by them.
There is a need in the art to provide an electronic driving circuit that will overcome at least in part the drawbacks of the prior art.